If you see an account on Instagram that belongs to someone who's passed away, you can report it to Instagram for memorialization. If you're an immediate family member of that person, you can request the account be removed from Instagram.
Memorializing the Instagram Account:
Instagram will memorialize the Instagram account of a deceased person if they receive a valid request. Their policy includes measures to prevent references to memorialized accounts from appearing on Instagram in ways that may be upsetting to the person's friends and family and to protect the privacy of the deceased person by securing the account.
Please keep in mind that they can't provide login information for a memorialized account. It's always against their policies for someone to log into another person's account.
Removing the Instagram Account:
Verified immediate family members may request the removal of a loved one’s account from Instagram. When you submit a request for removal, Instagram requires proof that you're an immediate family member of the deceased person, such as:
The deceased person's birth certificate
The deceased person's death certificate
Proof of authority under local law that you are the lawful representative of the deceased person, or his/her estate